Electronic packages, such as ceramic hybrid packages containing integrated circuits and/or power electronic components, are used in a wide variety of applications. For example, electronic packages are used in variable speed, constant frequency power generation systems. In a variable speed, constant frequency power generation system, a variable speed mechanical input, such as the engine of an aircraft, mechanically drives a generator at a variable speed. Because the generator is being driven at a variable speed, the frequency of its output signal is consequently variable. A variable speed, constant frequency power generation system converts the variable frequency output from a variable speed, mechanically driven generator into constant frequency alternating current for use by alternating current loads.
In a typical variable speed, constant frequency power generation system, a rectifier converts the variable frequency output from a variable speed, mechanically driven generator into a DC signal. An inverter then inverts the DC signal from the rectifier into constant frequency AC output power. Power transistors contained in electronic packages are often used as inverter switches in the inverter of such a variable speed, constant frequency power generation system in order to switch the DC signal, typically a high voltage DC signal, so as to produce pulses at the output of the inverter. These pulses are filtered to produce AC output power having a sinusoidal waveform. The widths of the pulses are typically modulated to regulate the magnitude of the AC output power. Because the power transistors in the inverter carry currents having large magnitudes, these power transistors generate substantial quantities of heat which, if not dissipated, may damage or destroy the power transistors.
Accordingly, the package containing such power electronics as the power transistors used in the inverter of a variable speed, constant frequency power generation system must be clamped or otherwise suitably fastened to a heat transfer surface of a heat sink. A heat sink typically includes a heat transfer surface and a heat exchanger through which cooling fluid flows to draw heat away from supported by the heat transfer surface of the heat sink. In the case of power transistors, the heat transfer surface draws sufficient heat away from the package of the power transistors to protect the power transistors from heat produced damage.
Furthermore, since an electronic package (which is a package containing electronic components such as power transistors) is often fabricated from ceramic, or similar, relatively fragile materials, the electronic package can be damaged by the clamping forces exerted on the electronic package by a clamping arrangement which clamps the electronic package to a heat sink (or other support surface). Thus, in clamping an electronic package to a heat sink, care must be exercised to ensure that these clamping forces are not excessive and are evenly distributed over the electronic package so as to reduce the tendency to fracture or otherwise damage the electronic package; yet, at the same time, an adequate clamping force must be applied to ensure proper thermal conductivity between the electronic package and the heat sink.
The clamping arrangement must also be designed to withstand and absorb any internal hydraulic pressure which may be exerted by the cooling fluid flowing through the heat exchanger of the heat sink on the electronic package; otherwise, this hydraulic pressure could damage the electronic package and/or the clamping arrangement.